Thanks to the those great folk at Element14 I was able to get my hands on a (free!) Raspberry Pi 2 today on the day of release.
Initial impressions are that this is indeed a much faster beast. The Pi boots quickly, the GUI opens almost immediately and the response time in Minecraft is (according to my sons) much improved.
I needed a more empirical test so I thought I'd set up the Pi2 to act as my online Minecard generator. Normally, on an old (can we really call them that now?) Model B it ran at at least 70% CPU utilisation and the whole image building process takes about 90 seconds (although that does include upload time).
I ported all the code over to me shiny new Pi2 and swapped the network cables. Simply building a new world in Minecraft is incredibly quick and does barely taxes the CPU about 10% (I've allocated 512M to the GPU). In terms of the entire image generation process itself, it was so obviously faster that I was able to remove almost all of the time.sleep() calls in the Python that I'd needed to ensure that all the various stages completed in the correct order.
The Pi2 builds and uploads an image in 33 seconds. At least a threefold increase in performance!
I've returned the original Model B to service for now, so that I can do some more tests on the Pi2.